Method for the boration of titanium and titanium alloys

ABSTRACT

Metals, especially titanium and titanium alloys, are borated with a borating agent prepared by annealing amorphous boron at a temperature between 850*C and 1,300*C in an inert gas, especially a noble gas. The boration is best accomplished by packing the metal into the borating agent and heating it to a temperature between 900*C and 1,400*C while passing a noble gas through the borating agent. Activators and inert substances can be added to the borating agents.

Ilnited States Patent [191 METHOD FOR THE DURATION OF TITANIUM ANDTITANIUM ALLOYS [75] Inventor: llelmut Eduard Kunst,

Osterholz-Scharmbeck, Germany [73] Assignee: Institut Furl-Iarterei-Technik,

Bremen-Lesum, Germany 22 Filed: 0ct.26, 1970 21 Appl.N0.:84,229

[51] Int. Cl. C23f 7/00 [58] Field of Search 148/63, 31.5, 20.3, 6;23/209; ll7/107.2 P, DIG. 10, 106; 423/298 [56] References Cited UNITEDSTATES PATENTS 5/1963 Commanday et al. 117/107.2 P 10/1960 Dorner117/107.2 P 5/1959 Llewelyn et al 117/1072 P ,Ian. 22, I974 2,528,45410/1950 Schlesinger et a1 117/DIG. 10 3,551,105 12/1970 Cooper 23/2093,029,162 4/1962 Samuel et a1. 148/63 2,949,390 8/1960 Feder et a1148/63 3,382,048 5/1968 Lindberg, Jr 23/204 R FOREIGN PATENTS ORAPPLICATIONS 851,208 10/1960 Great Britain 148/63 Primary ExaminerEdwardJ. Meros Attorney, Agent, or Firm-Sughrue, Rothwell et a1.

[5 7 ABSTRACT 5 Claims, No Drawings METHOD FOR THE BORATION OF TTTANIUMAND TITANIUM ALLOYS BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a borating agent as well as a methodfor the boration of metals, especially titanium and titanium alloys. Theinvention furthermore concerns work pieces made of titanium or titaniumalloys which are borated according to this method.

2. Description of the Prior Art The extensive use of titanium andtitanium alloys is thus far prevented, among other things, by the factthat there are no suitable methods known which are practical forincreasing the hardness and wear-and-tear resistance of the surface ofwork pieces made of titanium and titanium alloys, without at the sametime impairing the positive properties of the titanium (highstrengthweight ratio, good toughness, and good corrosion properties).

The invention accordingly is intended to propose a novel borating agentas well as a method for the boration of metals, especially titanium andtitanium alloys, which, through the indiffusion of boron considerablyimproves the hardness and wear-and-tear resistance of the surfaces ofwork pieces, especially made of titanium and titanium alloys, withoutimpairing the abovedescribed favorable properties of the work material.

SUMMARY OF THE INVENTION The borating agent according to the inventionconsists of a boron source, for example, a material containing boron, asa boron donor under a noble gas, especially argon (the verypurestargon), the boron here being amorphous and being annealed and thenagain cooled down.

DETAILED DESCRIPTION OF THE INVENTION The borating agent from theabove-described boron source when used is best provided with additives,more specifically, with suitable activators, especially alkali,alkalineearth-, or ammonium-halides, for example, ammonium chloride,ammonium fluoride, barium fluoride, sodium bromide, and the like. Thisactivator has the effect that the hardness layer, made with the boratingagent according to the invention, comes out thicker on the workingmaterial treated.

Furthermore, according to the invention, an inert substance, in otherwords, a substance that does not participate in the reaction, is addedto the borating agent. The following are particularly suitable for thispurpose: aluminum oxide, magnesium oxide, zirconium oxide, berylliumoxide, and other stable oxides, but also talc, asbestos, and the likecan be used. Such inert substances keep the borating agent in adisintegrated, gaspermeable state also during boration and make iteasier to take the borated work pieces out of the borating agent afterboration.

If, according to another embodiment of the invention, a noble gas,especially argon, is conducted through the borating agent during theboration of the work pieces, the inert substances facilitate the passageof the noble gas.

Borated work pieces, according to the invention, made of titanium ortitanium alloys, are provided with a surface layer which possesses asurface hardness of 3,000-3,500 I-IV kglmm In the experiments that wereconducted, this hardness was measured in the known manner according toVickers with a stress of 500 g. The thickness of this hardened surfacelayer is between 0.004 and 0.1 mm. It was furthermore ascertained thatthe hardened surface layer, made according to the invention, consists ofthe titanium borides TiB and TiB. This layer is hard and wear-and-tearproof, without the base working material that is, the titanium ortitanium alloy being made brittle due to the admission of oxygen,nitrogen, or hydrogen.

In detail, we proceed as follows in making the boron source, a componentof the borating agent: amorphous boron is annealed between 850C and l, l00C for a period of about 1-3 hours, with simultaneous constantconduction therethrough of a noble gas, especially argon (purest argon)and is then cooled, accompanied by further through-conduction of a noblegas, down to about room temperature. During this process, the amorphousboron is in a container that is sealed against the entry of air andagainst the entry of foreign gases; this container is provided with afeeder line'and an evacuation line for the noble gas.

The boron source can readily be used as a borating agent without anyfurther additives.

It is advantageous, however, to add the abovedescribed substances, thatis, an inert substance as a diluent, as well as an activator. Optimumconditions are obtained when the borating agent contains about 18-40percent of amorphous boron, treated in accordance with this invention,80 percent of the inert substance, and 2-8 percent of the activator.

Boration with the borating agent according to this invention is bestaccomplished by packing the work piece to be treated into the boratingagent in a suitable vessel and heating it to a temperature between 900and 1,400C in an oven. During boration, the noble gas, es-

pecially argon (purest argon), is constantly conducted through theborating agent. For this purpose the vessel is closed off against theentry of air and other foreign gases and it is provided with an inletand an outlet for the noble gas. The duration of the boration is atleast 3 hours. This is followed by a slow cooling of the workingmaterial.

EXAMPLE I 1 kg of amorphous boron was annealed for 2 hours, accompaniedby the conduction therethrough of argon, at a temperature of 1 ,000C.This was followed by cooling over a period of 3 hours, accompanied byfurther conduction therethrough of argon, down to about roomtemperature. This boron source was then used as the borating agent for awork piece of pure titanium.

The work piece was packed in the treated amorphous boron powder and wasborated for a period of 15 hours at a temperature of 1,000C. Duringboration, the argon was conducted through the borating agent. The workpiece thus treated had a hard surface layer with a thickness of 0.04 mmand a hardness of 3,0003,500 HV kg/mm EXAMPLE II 950 g of amorphousboron was treated as described in Example I above, in other words, itwas annealed. 50 g of barium fluoride was then admixed as an activatorinto the amorphous boron which had been cooled down to room temperature.Afterward, boration was performed over a period of 5 hours on a workpiece of pure titanium, accompanied by the conduction of argon throughthe borating agent, at a temperature of 1,300C. The layer thus producedon the work piece had a thickness of 0.07 mm with a hardness of3,0003,500 HV kg/mm EXAMPLE Ill 300 g of amorphous boron was once againtreated as described in Example I above. After cooling, 600 g ofaluminum oxide was added to the boron powder as an inert substance,along with 30 g of ammonium chloride as an activator which was likewisemixed in. With the borating agent thus produced, a work piece, made of atitanium alloy TiAl V was borated, more specifically, for a period of 5hours, while argon was being conducted through the borating agent, aswell as at a temperature of 1,200C. The layer produced here had athickness of 0.08 mm with a hardness of 3,0003,500 HV kg/mm What isclaimed is:

1. A method for borating a titanium metal workpiece which comprises:

contacting said titanium metal workpiece with a borating agent at atemperature of between 900 and 1400 C., for a period of at least 3 hourswhile simultaneously conducting a substantially pure noble gas throughthe borating agent, during bora- 4 tion,

said borating agent being prepared by a method which comprises:

annealing amorphous boron at a temperature of between 850 and 1 C, for aperiod ranging from about 1 to 3 hours, while simultaneously passing asubstantially pure noble gas therethrough, and subsequently, coolingsaid boron while simultaneously passing a substantially pure noble gastherethrough.

2. The method of claim 1 wherein said noble gas is argon.

3. The method of claim 1, wherein an activator is added to said boratingagent, said activator being a member selected from the group consistingof an alkali metal halide, an alkaline earth metal halide, and anammonium halide.

4. The method of claim 3, wherein said activator is a member selectedfrom the group consisting of ammonium chloride, ammonium fluoride,barium fluoride and sodium bromide.

5. The method of claim 1, wherein an inert substance is added to saidborating agent, said inert substance being a member selected from thegroup consisting of aluminum oxide, magnesium oxide, zirconium oxide,

beryllium oxide, talc and asbestos.

2. The method of claim 1 wherein said noble gas is argon.
 3. The methodof claim 1, wherein an activator is added to said borating agent, saidactivator being a member selected from the group consisting of an alkalimetal halide, an alkaline earth metal halide, and an ammonium halide. 4.The method of claim 3, wherein said activator is a member selected fromthe group consisting of ammonium chloride, ammonium fluoride, bariumfluoride and sodium bromide.
 5. The method of claim 1, wherein an inertsubstance is added to said borating agent, said inert substance being amember selected from the group consisting of aluminum oxide, magnesiumoxide, zirconium oxide, beryllium oxide, talc and asbestos.